This disclosure relates generally to the field of digital photography. More particularly, but not by way of limitation, this disclosure relates to still image stabilization techniques. As used herein, image stabilization refers to a collection of techniques for reducing motion-induced blurring during image capture operations. Such motion may result from the movement of the camera, objects in the scene, or both.
Taking high quality photographs in low ambient light conditions, or photographing dynamic scenes (e.g., sport scenes) is challenging due to camera motion and/or the motion of objects within a scene during image capture. One way to reduce motion blur without amplifying an image's noise is to capture and fuse multiple short exposed images of the scene. Such operations are often called ‘Still Image Stabilization.’ While shortening image exposure times can reduce motion blur artifacts, it does so at the expense of a noisier and/or darker image.
A common approach to image stabilization consists of (1) selecting a reference image from a set of multiple short exposed images, (2) globally registering all non-reference images with the reference image, and (3) synthesizing an output image by fusing all captured images to the reference image. In this way the output image represents the scene as it was at the time the reference image was captured, where non-reference images are used to reduce the noise in the reference image by averaging/merging multiple observations of each reference pixel across all images. A common approach to selecting the reference image is based on a quality criterion that is evaluated for each image independently (e.g., image sharpness). Such an approach can be insufficient because is does not account for, or consider, scene dynamics. For example, when capturing a dynamic scene various objects may have different relative positions in the different short exposure images. Selecting the reference image independent of the other images can result in a situation where the positions of the objects in the reference image are very different from their positions in the other images. In these situations, the image regions occupied by such objects in the reference frame cannot be improved because they have no corresponding counterparts in the other frames. Thus, it would be beneficial to provide a means to select a reference image so as to improve image stabilization operations.